Society is in a highly information-oriented system, and therewith there have been increasing social demand and importance of technologies and materials for information processing and recording. However, conventional digital optical (or magnetic) recording methods are considered to have a limitation of about 1 TB/inch2 even allowing for future development of technologies, and there is care that the technologies reach the limit within 5 to 10 years. Thus, it has been required to find a novel very high-density recording method, thereby establishing a technology capable of overcoming the limitation.
Holographic memories have been attracting much attention as one of ultra high-density and large capacity recording methods for meeting the demand of the society. The holographic memories can, record three-dimensional information by using light interference as it is, or convert two-dimensional planar information into a recording medium three-dimensionally. Particularly, recording and regenerating methods of two-dimensional page-data are highly compatible with signal processing systems of conventional digital recording methods and show fast transfer of the recording and regeneration, and thus have great potential and can achieve very high-capacity processing with high density exceeding 1 TB/inch2.
Photorefractive materials, photopolymerizable polymers (photopolymers), and organic photochromic materials (particularly polymers) are conventionally known as optical information recording media capable for holographic memory. The pbotorefractive materials, which include inorganic crystalline materials such as barium titanate and lithium niobate as typical ones, have disadvantages of poor sensitivity, fundamental difficulty of nondestructive readout, poor selectivity for writing light wavelength, brittle, poor processabilty, difficulty for thin film fabrication, etc. Further, the photopolymers are advantageous in that they can be relatively freely designed in view of reducing the disadvantages. However, materials using the photopolymers are not rewritable and can be used only for write-once media. Known as typical examples of the organic photochromic materials are polymers having an azobenzene structure, which are capable of information recording based on various physical principles by interference exposure, multiphoton reaction, localized heat excitation, surface modification, etc., and the molecular structures and functions of the polymers have been studied For example, photo-induced birefringence, hologram recording using the same, and usability of a copolymerized macromolecule material having a photoresponsive azobenzene moiety and a highly anisotropic liquid crystalline moiety have been reported in S. Xie, A. Natansohn and P. Rochon, Chem. Rev., vol. 5 (1993) p. 403-411, “Recent Development in Aromatic Azo Polymers Research”. 
Further, findings on hologram formation and relaxation dynamics in the copolymerized macromolecule material having the photoresponsive azobenzene moiety and the highly anisotropic liquid crystalline moiety have been reported in T. Bieringer, R. Wuttke, D. Haarer, U. Gesner and J. Rubner, Macromol. Chem. Phys., vol. 196 (1995) p. 1375-1390, “Relaxation of holographic gratings in liquid-crystalline side chain polymers with azo chromophores”. 
Furthermore, it has been reported that, in the azobenzene polymer, the orientation of the molecules can be controlled by irradiating a linearly polarized light to utilize birefringence distribution for information recording, and the orientation can be disarranged by a circularly polarized light to erase the information. Also the effects of dipole of the highly anisotropic copolymer component on the properties have been studied in A. Natansohn and P. Rochon, ACS Symposium Series, vol. 672 (1997) p. 236-250, “Azobenzene-containing polymers: digital and holographic storage” and A. Natansohn, P. Rochon, X. Meng, C. Barrett, T. Buffeteau, S. Bonenfant and M. Pezolet, Macromolecules, vol. 31 (1998) p. 1155-1161, “Molecular addressing Selective photoinduced cooperative motion of polar ester groups in copolymers containing azobenzene groups”. 
Further, a holographic recording material comprising a polymer with an azobenzene structure has been applied for a patent (WO 00/54111 (JP-T-2002-539475) and WO 00/54112 (JP-T-2002-539476), the term “JP-T” as used herein means a published Japanese translation of a PCT patent application). And compounds having an azo bond like the azobenzene structure have been studied in view of wider, various applications (JP-A-11-12242, JP-A-11-1688, JP-A-6-157511, and JP-A-11-312335).
However, a material satisfying all the various properties required for a practical application such as sensitivity, response speed, long-term storage stability, and repeatability have not found in these studies and proposals.